Bifunctional Catalyst NiFe-MgAl for Hydrogen Production from Chemical Looping Ethanol Reforming

Abstract

Ethanol, especially that produced from biomass, is considered as a renewable and carbon-neutral candidate to produce hydrogen. Performances of NiFe-MgAl bifunctional catalysts, in terms of activity, stability, and regenerability, in chemical looping reforming (CLR) of ethanol were studied. The NiFe-MgAl bifunctional catalysts were prepared from hydrotalcite-like compounds by the co-precipitation method. Various characterization techniques, that is, X-ray diffraction, inductively coupled plasma, nitrogen adsorption/desorption, H2-temperature-programmed reduction, and transmission electron microscopy, were used to determine properties of fresh and spent catalysts. In addition, O2 temperature-programmed oxidation, scanning electron microscopy, and Raman analyses were used for observation of coke formation on the spent catalysts. Meanwhile, in situ diffuse reflectance infrared Fourier transform spectroscopy can verify the evolution of the catalyst during the reactions. It was observed that the NiFe-MgAl catalyst showed higher catalytic activity and stability than the monometallic Fe-MgAl and Ni-MgAl catalysts. More specifically, the NiFe-MgAl catalyst provided the highest H2 concentration up to 80% at a low reaction temperature of 500 °C. This high performance was ascribed to the formation of Ni-Fe alloy particles. The combination of pulse experiments and X-ray photoelectron spectroscopy analysis elucidated that the iron particle at the surface was in the form of FeO that can oxidize the carbon deposits, resulting in the suppression of coke formation. In addition, the NiFe-MgAl catalyst can maintain high hydrogen selectivity for 10 repeated cycles.